1. Field of the Invention
The present invention relates to a canned motor for use with a pump actuatable thereby which is placed in a housing shared by the canned motor, and more particularly to a canned motor suitable for use in high-temperature, high-pressure environments at temperatures of 400.degree. C. or higher and under pressures of 200 kgf/cm.sup.2 or greater.
2. Description of the Prior Art
One conventional canned motor with a pressure-resistant structure is shown in FIGS. 1 and 2 of the accompanying drawings.
As shown in FIG. 1, the canned motor primarily comprises a rotor 2 fitted over a main shaft 1 and a stator 4 disposed around the rotor 2. A pump which can be actuated by the canned motor has an impeller (not shown) mounted on an end of an extension of the main shaft 1, which is rotatably supported by magnetic bearings. The stator 4 is fixedly supported in a cylindrical casing 3 having axially opposite end plates 13. The stator 4 comprises a stator core 7 of steel lamination and coil ends 8 which are housed in a space defined in the casing 3 and a stator can 15. The stator core 7 is mounted in the casing 3 hermetically covered by the stator can 15 in the form of a thin cylindrical wall covering an inner circumferential surface of the stator core 7.
The rotor 2 comprises a rotor core 5 of steel lamination and slot bar and a rotor can 6 in the form of a thin cylindrical wall covering an outer circumferential surface of the rotor core 5 and spaced slightly radially inwardly from the stator can 15.
The coil ends 8 project axially from axially opposite ends of the stator core 7, and are connected to windings 9 (see FIG. 2) disposed in the stator core 7.
As shown in FIG. 2, the stator core 7 has a plurality of slots 10 defined therein and successively positioned at given spaced intervals in the circumferential direction of the stator core 7. The slots 10 extend axially through the stator core 7 and have radially inner constricted ends 10b which are open at an inner circumferential surface of the stator core 7 and tapered portions 10c positioned slightly radially outwardly of the constricted open ends 10b. The windings 9, each comprising a plurality of twisted thin wires, are enclosed by sheets 11 of insulating paper and placed in respective winding chambers 10a in the respective slots 10. The windings 9 are retained in the winding chambers 10a against dislodgment therefrom by flat elongate wedge plates 12 of ceramics, for example, which are inserted into the respective tapered portions 10c.
Cylindrical coil end reinforcing tubes 14, each having an inside diameter which is the same as the inside diameter of the stator core 7, extend axially between the end faces of the stator core 7 and the end plates 13 of the casing 3. The stator can 15 is held against inner circumferential surfaces of the coil end reinforcing tubes 14 and the inner circumferential surface of the stator core 7. The stator can 15 prevents a fluid which is being handled by the pump from entering into the stator 4.
The stator can 15 is made of a cylindrical thin sheet of a metallic material such as a nickel alloy or the like, and has a small thickness ranging from about 0.2 to 1 mm. The stator can 15 is fixedly joined to the end faces of the stator core 7 and/or the end plates 13 of the casing 3 as by welding.
When an alternating current flows through the windings 9, the rotor 2 and the main shaft 1 rotate in unison with each other, causing the pump impeller to rotate for thereby pumping a fluid. Part of the fluid that is being handled by the pump is introduced into a gap between the rotor 2 and the stator 4 which are covered with the rotor can 6 and the stator can 15, respectively, thereby cooling the rotor 2 and the stator 4.
When the fluid being handled by the pump is subjected to a very high pressure such as of 200 kgf/cm.sup.2 or higher, for example, the fluid introduced into the gap between the rotor 2 and the stator 4 exerts forces tending to press the stator can 15 into the slots 10. Therefore, portions of the stator can 15 forcibly project into the slots 10 through the constricted open ends 10b. The stator can 15 is thus liable to be damaged by edges of the constricted open ends 10b, and to push the wedge plates 12 for thereby displacing the windings 9, which may possibly suffer an insulation failure.
The coil end reinforcing tubes 14 have to be relatively thin because the coil ends 8 are inserted therethrough. When the coil end reinforcing tubes 14 are subject to a high pressure, they are easily deformed particularly at their ends, developing steps at their junctions to the stator core 7. Those developed steps expose corners of the stator core 7 which tend to cause damage to the stator can 15. The coil end reinforcing tubes 14 may be prevented from being deformed if they have an increased wall thickness for their sufficient mechanical strength. However, the wall thickness of the coil end reinforcing tubes 14 cannot be substantially increased due to limitations imposed by the shape of the slots 10 in the stator core 7 and the insertion of the coil ends 8.